Radiological Diagnosis

Lissencephaly

Discussion

[Figure1],[Figure - 2] show thickened cortex with broad, flat gyri, smooth gray-white matter interface and shallow sylvian fissures, giving a figure of eight appearance. The neuronal and glial precursors are generated in the germinal matrix that outlines the lateral and 3rd ventricles in the seventh gestational week. These neurons migrate along the radial glial fibres that extend from the ventricles to the brain surface [1]. Disruption of this normal process of normal generation and cellular migration results in a spectrum of brain malformations [2]. These are divided into several types, depending on the timing and everity of the arrest of neuronal migration [1]. Lissencephaly or smooth brain refers to brain with absent or poor sulcation. It can be complete (synonymous with agyria-pachygria or nonlissencephalic cortical dysplasia). Intrauterine infections such as TORCH can also result in a smooth lissencephalic - appearing brain.

Imaging features have been subdivided into three types based upon the severity of the disorder.

Type-1 Lissencephaly shows colpocephaly and a thickened cortex with broad, flat gyri, smooth gray-white matter interface, and straight oblique or shallow sylvian fissures, giving a figure of eight appearance [3].

Type - II is being described as an agyric, severelydisorganised unlayered cortex with poor corticomedullary demarcaton [4]. MR studies in these patients show thickened cortex that has a polymicrogyric appearance associated with hypomyelination of the underlying white matter.

Type - III of lissencephaly, the cerebrocerebellar type, occurs without a figure of eight configuration but has microcephaly, moderately thickened cerebral cortices, enlarged ventricles and hypoplastic cerebellum and brainstem [3].

Associated abnormalities include: Walker Warburg syndrome which is characterized by ocular malformations, cephalocele and profound congenital hypotonia [4]. Miller Dicker Syndrome is associated Type - I Lissencephaly.